Planar optical waveguide, optical chip, optical module and optical communication system

Abstract

The invention provides a planar optical waveguide, which comprises a substrate, a sacrificial layer and a core layer which are sequentially arranged from bottom to top, and is characterized in that the sacrificial layer comprises at least one air cavity, and the air cavity penetrates from the bottom surface of the sacrificial layer to the top surface of the sacrificial layer; and the core layer comprises a polarization rotation beam splitter. Therefore, the sacrificial layer comprising the air cavity is arranged below the core layer, so that the polarization rotation beam splitter is suspended relative to the substrate, a medium with a low refractive index is formed through air in the air cavity, the refractive index difference between the sacrificial layer and the core layer is increased, and signal light is limited in the core layer to be transmitted; the performance of the polarization rotation beam splitter is improved, and the size of the polarization rotation beam splitter is effectively reduced.

Description

Technical Field

[0001] This application relates to the field of optical communication, and specifically, to a planar optical waveguide, an optical chip, an optical module, and an optical communication system. Background Art

[0002] Polarization multiplexing technology is an optical communication technology that uses two orthogonal polarization states of light to transmit information simultaneously, thereby improving the optical communication capacity. A polarization splitter-rotator (PSR) is a key passive device for implementing polarization multiplexing technology. The polarization splitter-rotator consists of a polarization rotator and a polarization beam splitter. The polarization rotator is used for the polarization state conversion of the signal light, and the polarization beam splitter is used for the separation of the signal light. With the improvement of the integration degree of optical chips and the requirements of system size reduction and packaging simplification, the PSR functional device has gradually changed from a discrete optical glass to a miniaturized and integrated planar optical waveguide form.

[0003] Among them, there are already various design schemes for the planar optical waveguide structure of PSR in terms of function. However, in the current optical chip platform, such as the optical chip platform based on indium phosphide (InP) material, the fabricated waveguide has weak confinement, and it is unable to effectively confine light to propagate in the waveguide. Therefore, a larger chip size is required to ensure the device performance. Therefore, how to implement a PSR planar optical waveguide scheme with small size and high performance is an urgent problem to be solved. Summary of the Invention

[0004] This application provides a planar optical waveguide structure. By providing a sacrificial layer including an air cavity under the core layer, the polarization splitter-rotator is suspended relative to the substrate, while improving the performance of the polarization splitter-rotator, effectively reducing the size of the polarization splitter-rotator.

[0005] In a first aspect, a planar optical waveguide is provided, including, sequentially arranged from bottom to top: a sacrificial layer including at least one air cavity, and the air cavity penetrates from the bottom surface of the sacrificial layer to the top surface of the sacrificial layer; a core layer including a polarization splitter-rotator. Thus, by providing a sacrificial layer including an air cavity under the core layer, the polarization splitter-rotator is suspended relative to the substrate. The air in the air cavity forms a low-refractive-index medium, increasing the refractive index difference between the cladding and the core layer, thereby effectively confining the signal light to propagate in the core layer. While improving the performance of the polarization splitter-rotator, the size of the polarization splitter-rotator is effectively reduced.

[0006] In combination with the first aspect, in some implementations of the first aspect, where: an upper cladding is further provided in the planar optical waveguide, the upper cladding is located above the core layer, and the refractive index of the upper cladding is less than that of the core layer; and / or a lower cladding is further provided in the planar optical waveguide, the lower cladding is located between the core layer and the sacrificial layer, and the refractive index of the lower cladding is less than that of the core layer. Thus, a refractive index difference is formed among the upper cladding, the lower cladding, and the core layer, effectively restricting the signal light to be transmitted in the core layer and reducing the overall size of the polarization rotation beam splitter.

[0007] In combination with the first aspect, in some implementations of the first aspect, where: at least one etching hole is provided in the planar optical waveguide, and the etching hole penetrates from the top surface of the planar optical waveguide to the top surface of the sacrificial layer. Thus, a channel for the etching solution is opened through the etching hole, and an air cavity is formed in the sacrificial layer.

[0008] In combination with the first aspect, in some implementations of the first aspect, on the substrate, the projection of the core layer covers the projection of the air cavity. Thus, by utilizing the stress effect between the core layer and the sacrificial layer, the core layer plays a supporting role above the sacrificial layer, ensuring mechanical robustness in the planar optical waveguide structure with an air cavity provided.

[0009] In combination with the first aspect, in some implementations of the first aspect, a support layer is further provided in the planar optical waveguide, the support layer is located above the core layer, the support layer is at least partially in contact with the core layer, and on the substrate, the projection of the support layer covers the projection of the air cavity. Thus, by utilizing the stress effect between the support layer and the core layer, it plays a supporting role above the sacrificial layer, ensuring mechanical robustness in the planar optical waveguide structure with an air cavity provided.

[0010] In combination with the first aspect, in some implementations of the first aspect, the polarization rotation beam splitter includes a first transmission waveguide, a mode conversion waveguide, a second transmission waveguide, and a third transmission waveguide, where: the first transmission waveguide is connected to the first end face of the mode conversion waveguide; the second transmission waveguide is connected to the second end face of the mode conversion waveguide; the projection of the second transmission waveguide on the first plane overlaps with the projection of the third transmission waveguide, the first plane is perpendicular to the plane where the substrate is located, and the first plane is parallel to the light transmission direction of the polarization rotation beam splitter. Thus, by designing the structures of the first transmission waveguide, the mode conversion waveguide, the second transmission waveguide, and the third transmission waveguide, the mode of the signal light is converted, realizing the function of the polarization rotation beam splitter.

[0011] In some implementations, the first transmission waveguide is used to input the first signal light. The second transmission waveguide is used to output the second signal light, and the third transmission waveguide is used to output the third signal light. Alternatively, the first transmission waveguide is used to output the first signal light, the second transmission waveguide is used to input the second signal light, and the third transmission waveguide is used to input the third signal light. Among them, the first signal light includes the signal light of the first mode and the signal light of the second mode, the second signal light is of the first mode, and the third signal light is of the first mode. Among them, the signal light of the first mode and the signal light of the second mode are orthogonal.

[0012] In some implementations: The first transmission waveguide is used to input the first signal light to the first end face of the mode conversion waveguide. The first signal light includes the signal light of the first mode and the signal light of the second mode. The mode conversion waveguide is used to transmit the signal light of the first mode incident from the first end face to the second end face. The mode conversion waveguide is also used to convert the signal light of the second mode incident from the first end face into the fourth signal light and transmit the fourth signal light to the second end face. Among them, the fourth signal light is of the first mode, and there is a phase difference between the fourth signal light and the second signal light. The second transmission waveguide is used to receive and transmit the signal light of the first mode emitted from the second end face, so that the second signal light is output from the second transmission waveguide. The third transmission waveguide is used to receive the fourth signal light and convert the fourth signal light into the third signal light, so that the third signal light is output from the third transmission waveguide. Among them, the second signal light and the third signal light have the same phase.

[0013] Combined with the first aspect, in some implementations of the first aspect, the cross-section of the mode conversion waveguide parallel to the substrate direction includes a trapezoidal region. And in the waveguide part of the mode conversion waveguide corresponding to the trapezoidal region, the cross-section parallel to the direction of the second end face is a stepped structure. Through the design of the stepped structure, the symmetry in the vertical direction of the waveguide is broken, so that a hybrid polarization mode is introduced within a small waveguide width, the conversion efficiency of the signal light is improved, and the size of the mode conversion waveguide is further reduced.

[0014] Combined with the first aspect, in some implementations of the first aspect, the width of the third end face of the second transmission waveguide is greater than the width of the fourth end face, where the third end face is the end face connected to the mode conversion waveguide, and the fourth end face is the end face far from the mode conversion waveguide. Thus, through the narrowing of the width of the second transmission waveguide, the crosstalk between the second transmission waveguide and the third transmission waveguide is further reduced, and the extinction ratio of the polarization mode is improved.

[0015] In combination with the first aspect, in certain implementations of the first aspect, in a cross-section of the core layer parallel to the substrate, the second transmission waveguide includes a first trapezoidal region, and the third transmission waveguide includes a second trapezoidal region, where one base of the first trapezoidal region is connected to the second end face, the first waist of the first trapezoidal region is parallel to the second waist of the second trapezoidal region, and the first waist and the second waist are adjacent. By setting the adjacent sides of the coupling region between the second transmission waveguide and the third transmission waveguide to be parallel, the coupling length is extended, preventing the polarization rotation beam splitter from being affected by process tolerances such as waveguide width and waveguide topography near the coupling region, which affects the performance, and realizing a structural design solution for a polarization rotation beam splitter with high processing tolerance.

[0016] In combination with the first aspect, in certain implementations of the first aspect, the first trapezoidal region and the second trapezoidal region are isosceles trapezoids. That is, the first trapezoidal region and the second trapezoidal region have the same pattern shape and are arranged in opposite settings, thereby lengthening the coupling length and realizing a structural design solution for a polarization rotation beam splitter with high processing tolerance.

[0017] In a second aspect, a method for manufacturing a planar optical waveguide is provided for manufacturing the planar optical waveguide of the first aspect and any possible implementation thereof.

[0018] In a third aspect, an optical chip is provided, including an orthogonal modulator and the planar optical waveguide of the first aspect and any possible implementation thereof. The orthogonal modulator is used to modulate the signal light to transmit two paths of signal light to the polarization rotation beam splitter. The two paths of signal light are the second signal light and the third signal light respectively. The second signal light is in the first mode, and the third signal light is in the first mode. The polarization rotation beam splitter is used to receive the second signal light and the third signal light and combine the second signal light and the third signal light to output the first signal light. The first signal light includes the signal light in the first mode and the signal light in the second mode.

[0019] In a fourth aspect, an optical chip is provided, including a coherent receiver and the planar optical waveguide of the first aspect and any possible implementation thereof. Among them, the coherent receiver may specifically include a first coherent receiving unit and a second coherent receiving unit. The polarization rotation beam splitter is used to receive the first signal light. The first signal light includes the signal light in the first mode and the signal light in the second mode, and split the first signal light into two paths to output the second signal light and the third signal light. Among them, the second signal light is in the first mode, the third signal light is in the first mode, and the second signal light and the third signal light may carry the same or different information. The second signal light among them is received by the first coherent receiving unit, and the third signal light is received by the second coherent receiving unit. The coherent receiver is used to demodulate the second signal light and the third signal light to obtain the electrical signal corresponding to the second signal light and the electrical signal corresponding to the third signal light.

[0020] In a fifth aspect, an optical module is provided, which includes a light source, a signal generation chip, and the optical module according to the third aspect and any possible implementation thereof; and / or a signal processing chip, and the optical module according to the fourth aspect and any possible implementation thereof. Among them, the light source is used to input a light beam into the quadrature modulator in the optical chip. The signal generation chip is used to input an electrical signal into the quadrature modulator, and the electrical signal is used to modulate the light beam input into the quadrature modulator to generate a second signal light and a third signal light carrying information. The second signal light and the third signal light carrying information are input into a polarization rotation beam splitter, and the polarization rotation beam splitter is used to combine the second signal light to output a first signal light including a first mode and a second mode. And / or the polarization rotation beam splitter is used to receive the first signal light including the first mode and the second mode to output the second signal light and the third signal light carrying information, the second signal light is the first mode, and the third signal light is the first mode. The coherent receiver is used to convert the second signal light into a first electrical signal and convert the third signal light into a second electrical signal. The signal processing chip is used to process the first electrical signal and the second electrical signal to obtain the information carried in the second signal light and the information carried in the third signal light.

[0021] In a sixth aspect, an optical system is provided, which includes an optoelectronic device and the optical module according to the fifth aspect and any possible implementation thereof. Among them, the optoelectronic device is connected to the optical module, and the optoelectronic device is any one of an optical switch, an optical fiber router, and an optical fiber network card. Description of the Drawings

[0022] Figure 1 It is a schematic structural diagram of a planar optical waveguide provided by an embodiment of the present application.

[0023] Figure 2 It is a schematic flow chart of preparing a planar optical waveguide provided by an embodiment of the present application.

[0024] Figure 3 It is a top view of a planar optical waveguide structure provided by an embodiment of the present application.

[0025] Figure 4 It is a schematic structural diagram of a polarization rotation beam splitter provided by an embodiment of the present application.

[0026] Figure 5 It is a schematic structural diagram of a mode conversion waveguide structure in a polarization rotation beam splitter provided by an embodiment of the present application.

[0027] Figure 6 It is a schematic structural diagram of another mode conversion waveguide structure in a polarization rotation beam splitter provided by an embodiment of the present application.

[0028] Figure 7It is a schematic structural diagram of a second transmission waveguide and a third transmission waveguide in a polarization rotation beam splitter provided by an embodiment of the present application.

[0029] Figure 8 It is a schematic structural diagram of a second transmission waveguide and a third transmission waveguide in a polarization rotation beam splitter provided by an embodiment of the present application.

[0030] Figure 9 It is an optical chip provided by an embodiment of the present application.

[0031] Figure 10 It is an optical module provided by an embodiment of the present application.

[0032] Figure 11 It is an optical communication device provided by an embodiment of the present application. Detailed implementation manners

[0033] Next, the technical solutions in the present application will be described with reference to the accompanying drawings.

[0034] Hereinafter, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0035] The reference to "an embodiment" or "some embodiments" etc. described in this specification means that a specific feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the present application. Thus, the phrases "in an embodiment", "in some embodiments", "in other some embodiments", "in still other embodiments" etc. that appear in different places in this specification are not necessarily all referring to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "comprise", "include", "have" and their variants all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0036] In the description of the embodiments of the present application, the orientation or positional relationship indicated by the terms "upper", "lower", "vertical", "horizontal", etc. is defined with respect to the orientation or position in which the components in the drawings are schematically placed. It should be understood that these directional terms are relative concepts, and they are used for relative description and clarification, rather than indicating or implying that the indicated device or component must have a specific orientation, or be constructed and operated in a specific orientation. It can change accordingly with the change of the orientation in which the components in the drawings are placed, and thus cannot be construed as a limitation to the present application.

[0037] As used in the embodiments of the present application described below, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units need not be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0038] In the embodiments of the present application, words such as "exemplary" or "for example" are used to represent examples, illustrations, or explanations. Embodiments or design solutions described as "exemplary" or "for example" should not be construed as being more preferred or having more advantages than other embodiments or design solutions. The use of words such as "exemplary" or "for example" is intended to present relevant concepts in a specific manner for easy understanding.

[0039] In the embodiments of the present application, the same reference numeral is used to represent the same component or the same part. Additionally, the components in the drawings are not drawn to scale, and the dimensions and sizes of the components shown in the drawings are only exemplary and should not be construed as a limitation to the present application.

[0040] Polarization multiplexing technology is an optical communication technology that uses two orthogonal polarization states of light (such as horizontal and vertical) to simultaneously transmit information, thereby increasing the optical communication capacity. A polarization splitter-rotator (PSR) is a key passive device for implementing polarization multiplexing technology. The polarization splitter-rotator is composed of a polarization rotator and a polarization beam splitter. The polarization rotator is used for the polarization state conversion of the signal light, and the polarization beam splitter is used for the separation of the signal light. With the improvement of the integration degree of optical chips and the requirements of system size reduction and packaging simplification, PSR functional devices are gradually changing from the form of discrete optical glass to the form of miniaturized and integrated planar optical waveguides.

[0041] Among them, regarding the planar optical waveguide structure of PSR, there are already various design solutions in terms of function. However, in current optical chip platforms, such as optical chip platforms based on indium phosphide (InP) materials, the fabricated waveguides have weak confinement, and it is impossible to effectively confine light to propagate in the waveguides. Therefore, a larger chip size is required to ensure the device performance. Therefore, how to implement a small-size and high-performance PSR planar optical waveguide solution is an urgent problem to be solved.

[0042] In view of this, the present application provides a planar optical waveguide structure. By providing a sacrificial layer including an air cavity under the core layer, the polarization splitter-rotator is suspended relative to the substrate, effectively reducing the size of the polarization splitter-rotator while improving its performance.

[0043] Figure 1It is a schematic structural diagram of a planar optical waveguide provided by an embodiment of the present application. As Figure 1 shown, the planar optical waveguide includes a substrate 110, a sacrificial layer 120, and a core layer 130 arranged in sequence from bottom to top.

[0044] Among them, the substrate 110 can be composed of a single-layer material as the base of the planar optical waveguide, or the substrate 110 can be composed of multiple-layer materials, that is, one or more buffer layers are provided on the bottom layer as a whole of the substrate 110.

[0045] The sacrificial layer 120 includes at least one air cavity 121, and the air cavity 121 penetrates from the bottom surface of the sacrificial layer 120 to the top surface of the sacrificial layer 120.

[0046] The core layer 130 includes a polarization rotation beam splitter.

[0047] In the planar optical waveguide structure as Figure 1 shown, by providing a sacrificial layer including an air cavity under the core layer, the polarization rotation beam splitter is suspended relative to the substrate, and a medium with a low refractive index is formed by the air in the air cavity, increasing the refractive index difference between the core layer and the cladding layer, so as to confine the signal light to be transmitted in the core layer. While improving the performance of the polarization rotation beam splitter, the size of the polarization rotation beam splitter is effectively reduced.

[0048] Among them, the specific structure of the air cavity 121 is determined in combination with the actual etching process. For example, as Figure 1 shown in (a), the sacrificial layer 120 may only include one air cavity. Or, as Figure 1 shown in (b), it may include multiple air cavities, and among them, the multiple air cavities may be connected or not connected, which is determined according to the etching degree.

[0049] In some implementation manners, the material of the substrate 110 is InP. When the substrate 110 is composed of multiple-layer materials, the material of the bottom layer may be InP, and one or more buffer layers above the bottom layer may be InP materials or InP-based quaternary compounds. For the optical chip platform of InP materials, the fabricated waveguides have weak confinement, and it is impossible to effectively confine light to propagate in the waveguides. Therefore, a larger chip size is required to ensure the performance of the device. Using the planar optical waveguide structure of the present application, a PSR planar optical waveguide solution based on InP materials with small size and high performance can be realized. Usually, the size of the PSR planar optical waveguide of InP materials is about 2 mm, while using the planar optical waveguide provided by the present application, the size can be reduced to 600 - 1000 μm.

[0050] In some implementation manners, the planar optical waveguide structure can be as Figure 1As shown in (a) and (b), it is composed of a substrate 110, a sacrificial layer 120, and a core layer 130. At this time, the bottom surface of the air cavity 121 is in contact with the substrate 110, and the top surface of the air cavity 121 is in contact with the core layer 130. At this time, the air filled in the air cavity 121 in the sacrificial layer 120 serves as the lower cladding, and the air above the core layer 130 serves as the upper cladding. The refractive index of air is about 1, which is the smallest among various media. There is the largest refractive index difference between the air lower cladding, the air upper cladding and the core layer, so as to effectively confine the signal light to be transmitted in the core layer and reduce the overall size of the polarization rotation beam splitter.

[0051] In some implementation manners, the planar optical waveguide structure may be as Figure 1 As shown in (c), (d), (e) and (f), it is composed of a substrate 110, a sacrificial layer 120, a lower cladding 141, a core layer 130, and an upper cladding 142. At this time, the bottom surface of the air cavity 121 is in contact with the substrate 110, and the top surface of the air cavity 121 is in contact with the upper cladding 142. Among them, the lower cladding 141 is composed of a material with a refractive index less than that of the core layer 130. The upper cladding 142 is composed of a material with a refractive index less than that of the core layer 130. For example, the lower cladding 141 and the upper cladding 142 may be made of InP, and the core layer 130 may be made of materials such as InGaAlAs and InGaAsP. Thus, a refractive index difference is formed between the upper cladding, the lower cladding and the core layer, effectively confining the signal light to be transmitted in the core layer and reducing the overall size of the planar optical waveguide.

[0052] In some implementation manners, the planar optical waveguide structure may be composed of a substrate, a sacrificial layer, a lower cladding, and a core layer, and air is used as the upper cladding. Among them, the lower cladding may be made of InP, and the core layer may be made of materials such as InGaAlAs and InGaAsP. At this time, the bottom surface of the air cavity is in contact with the substrate, and the top surface of the air cavity is in contact with the lower cladding. Thus, a refractive index difference is formed between the air upper cladding, the lower cladding and the core layer, effectively confining the signal light to be transmitted in the core layer and reducing the overall size of the planar optical waveguide.

[0053] In some implementation manners, such as Figure 1 As shown in (f), a cutoff layer 122 is provided between the substrate 110 and the sacrificial layer 120. A cutoff layer 123 is provided between the sacrificial layer 120 and the lower cladding 141, or, in the case where the lower cladding 141 is not provided, a cutoff layer 123 is provided between the sacrificial layer 120 and the core layer 130. At this time, the bottom surface of the air cavity 121 is in contact with the cutoff layer 122, and the top surface of the air cavity is in contact with 123. Thus, the etching situation of the sacrificial layer is precisely controlled through the setting of the cutoff layer.

[0054] In some implementation manners, the planar optical waveguide structure may be as Figure 1As shown in (a), (b), and (c), on the substrate 110, the projection of the core layer 130 covers the projection of the air cavity 121. In particular, in the case where no support layer is provided in the planar optical waveguide structure, the stress between the core layer and the sacrificial layer can be utilized to enable the core layer to support above the sacrificial layer, ensuring mechanical robustness in the planar optical waveguide structure with an air cavity provided. At this time, the planar optical waveguide structure can also be understood as a shallow ridge waveguide, that is, a planar optical waveguide structure where the core layer is not completely etched. In some implementation manners, the planar optical waveguide structure can be as Figure 1 shown in (d), (e), and (f). On the substrate 110, the projection of the core layer 130 does not cover the projection of the air cavity 121. At this time, the planar optical waveguide structure can also be understood as a deep ridge waveguide, that is, a planar optical waveguide structure where the core layer is completely etched.

[0055] In some implementation manners, as Figure 1 shown in (e), a support layer 150 is further provided in the planar optical waveguide. The support layer 150 is located above the core layer 130. On the substrate, the projection of the support layer 150 covers the projection of the air cavity, and the support layer 150 is at least partially in contact with the core layer 130. Thus, the stress between the support layer and the core layer is utilized to support above the sacrificial layer, ensuring mechanical robustness in the planar optical waveguide structure with an air cavity provided. Among them, the support layer 150 can be composed of materials such as SiN, SiO, SiNO, etc. Among them, the support layer 150 being located above the core layer 130 can specifically mean that the support layer 150 is located on the top surface of the core layer 130. Or it can also mean that an upper cladding layer is further provided between the support layer 150 and the core layer 130, and the core layer 130, the upper cladding layer, and the support layer 150 are arranged in sequence from bottom to top. It is specifically determined according to the actual situation, and the present application does not limit this.

[0056] Figure 2 is a schematic flowchart of a method for preparing a planar optical waveguide provided by an embodiment of the present application. As Figure 2 shown, the method can include steps (a)-(d). It should be understood that the following steps specifically take the preparation of the planar optical waveguide structure as shown in Figure 1 (e) as an example. When preparing other planar optical waveguides provided by the present application, the steps shown in Figure 2 can be modified and replaced according to the specific structure.

[0057] (a) Grow a multi-layer epitaxial structure on the substrate. The multi-layer epitaxial structure can include a substrate 210, a sacrificial layer 220, a lower cladding layer 241, a core layer 230, and an upper cladding layer 242. Among them, the material of the substrate 210 can be InP. The material of the sacrificial layer 220 can be InGaAlAs or InGaAsP. The materials of the lower cladding layer 241 and the upper cladding layer 242 can be InP.

[0058] (b) Define the pattern of the polarization rotation beam splitter on the surface of the epitaxial structure by lithography, and etch the epitaxial structure. Specifically, the overall waveguide width of the polarization rotation beam splitter can be limited to W by the pattern 0 , and waveguide etching with a depth of h 1 is performed to form a polarization rotation beam splitter in the core layer 230.

[0059] (c) Etch at least one etching hole 260 from the top surface of the planar optical waveguide structure. The etching hole penetrates through the top surface of the planar optical waveguide to the top surface of the sacrificial layer 220. For example, in the case where the planar optical waveguide structure includes an upper cladding 242 and a lower cladding 241 as in Figure 2 , the etching hole 260 can penetrate from the top surface of the upper cladding 242 to the bottom surface of the lower cladding 241, that is, the etching hole depth is h 1 + h 2 . In addition, in the case where the planar optical waveguide structure only includes a substrate, a sacrificial layer, and a core layer, the etching hole can penetrate from the top surface of the core layer to the top surface of the sacrificial layer. Other cases can be specifically determined in combination with the planar optical waveguide structure and will not be elaborated here. Figure 3 The top view of the planar optical waveguide structure is shown. In the cross-section of the core layer along the direction parallel to the substrate, at least one etching hole 310 can be located on the periphery of the polarization rotation beam splitter.

[0060] (d) Etch the sacrificial layer through the etching hole 260 to form an air cavity. That is, a channel for the etching solution is opened through the etching hole 260, and by combining dry etching technology and wet etching technology, all the layers above the sacrificial layer 220 are removed, and an air cavity with a depth of h 3 is etched in the sacrificial layer. The structure of the air cavity is determined in combination with the specific etching situation. For example, the inside of the sacrificial layer can be completely hollowed out to form an air cavity. Or for the case of Figure 1 (b), multiple connected or unconnected air cavities are formed.

[0061] (e) Grow a support layer 250 on the top surface of the planar optical waveguide structure. Among them, the support layer 250 can be made of SiN, SiO, or SiNO materials.

[0062] In addition, the present application also provides the structure of the polarization rotation beam splitter as shown in Figures 4 to 7 . Through structural design, efficient mode conversion in the polarization rotation beam splitter is achieved, thereby reducing the size of the planar optical waveguide. The polarization rotation beam splitter as shown in Figures 4 to 7 can be applied to the combination with the planar optical waveguide structure described in Figure 1 , or applied to other planar optical waveguide structures. The present application does not limit this.

[0063] Figure 4It is a schematic structural diagram of a polarization rotation beam splitter provided by an embodiment of the present application. The polarization rotation beam splitter is composed of a first transmission waveguide 410, a mode conversion waveguide 420, a second transmission waveguide 431, and a third transmission waveguide 432.

[0064] Among them, the first transmission waveguide 410 is connected to the first end face of the mode conversion waveguide 420, the second transmission waveguide 431 is connected to the second end face of the mode conversion waveguide 420, the projection of the second transmission waveguide 431 on the first plane overlaps with the projection of the third transmission waveguide 432, the first plane is perpendicular to the plane where the substrate is located, and the first plane is parallel to the light transmission direction of the polarization rotation beam splitter.

[0065] In some implementation manners, such as Figure 4 as shown in (a) of, the second transmission waveguide 431 and the third transmission waveguide 432 are connected to the second end face of the mode conversion waveguide 420. That is, one end of the second transmission waveguide 431 is connected to the second end face of the mode conversion waveguide 420, and one end of the third transmission waveguide 432 is connected to the second end face of the mode conversion waveguide 420.

[0066] In some implementation manners, such as Figure 4 as shown in (b) of, the second transmission waveguide 431 is connected to the second end face of the mode conversion waveguide 420, the second transmission waveguide 431 and the third transmission waveguide 432 are arranged at intervals, and the third transmission waveguide 432 and the mode conversion waveguide 420 are arranged at intervals.

[0067] Among them, the mode conversion waveguide 420 can also be understood as a polarization rotator, a mode conversion part, or a mode rotation part. The mode conversion waveguide can be a wedge waveguide structure, and the wedge waveguide can be a common linearly tapered wedge waveguide or a special linearly asymmetric wedge waveguide. Or, it can also be understood that the cross-section of the mode conversion waveguide 420 along the direction parallel to the substrate is a trapezoid, and the trapezoid can be an isosceles trapezoid or a non-isosceles trapezoid. Among them, the combination of the second transmission waveguide 431 and the third transmission waveguide 432 can be understood as a polarization beam splitter, a mode separation part, or a mode coupling part, or can be understood as a coupler with two ports, and its structural form can be specifically in forms such as Y-branch, multimode interferometer, and asymmetric directional coupler.

[0068] In a polarization rotation beam splitter, the first transmission waveguide 410 is used to input the first signal light. The second transmission waveguide 431 is used to output the second signal light, and the third transmission waveguide 432 is used to output the third signal light. Alternatively, the first transmission waveguide 410 is used to output the first signal light, the second transmission waveguide 431 is used to input the second signal light, and the third transmission waveguide 432 is used to input the third signal light. Among them, the first signal light includes the signal light of the first mode and the signal light of the second mode, the second signal light is of the first mode, and the third signal light is of the first mode. Among them, the signal light of the first mode and the signal light of the second mode are orthogonal. The first mode and the second mode are specifically determined according to the actual structure design.

[0069] As a possible working form of a polarization rotation beam splitter: the first transmission waveguide 410 is used to input the first signal light to the first end face of the mode conversion waveguide 420, and the first signal light includes the signal light of the first mode and the signal light of the second mode. The mode conversion waveguide 420 is used to transmit the signal light of the first mode incident from the first end face to the second end face. The mode conversion waveguide 420 is also used to convert the signal light of the second mode incident from the first end face into the fourth signal light and transmit the fourth signal light to the second end face, where the fourth signal light is of the first mode, and there is a phase difference between the fourth signal light and the second signal light. The second transmission waveguide 431 is used to receive and transmit the signal light of the first mode exiting from the second end face, so that the second signal light is output from the second transmission waveguide. The third transmission waveguide 432 is used to receive the fourth signal light and convert the fourth signal light into the third signal light, so that the third signal light is output from the third transmission waveguide 432, where the second signal light and the third signal light have the same phase.

[0070] For example Figure 4Taking the case in [as an example], the first mode can be the transverse magnetic fundamental mode (TM0), and the second mode can be the transverse electric fundamental mode (TE0). Through the size design of the mode conversion waveguide 420, after the first signal light including the TM0 and TE0 modes is input into the first transmission waveguide 410, the signal light of the TE0 mode in the first signal light does not satisfy the phase matching condition, and the mode conversion waveguide 420 only serves as an ordinary transmission waveguide. Therefore, after passing through the mode conversion waveguide 420, the second transmission waveguide can output the second signal light of the TE0 mode. The signal light of the TM0 mode in the first signal light will undergo adiabatic mode conversion in the mode conversion waveguide 420 and output from the mode conversion waveguide 420 in the TE1 mode with a half-wavelength phase difference from the TE0 mode. Since the phase matching condition is satisfied at the position of the third transmission waveguide 432, it enters the third transmission waveguide 432 and finally outputs from the third transmission waveguide 432 as the third signal light of the TE0 mode.

[0071] As another possible working form of the polarization rotation beam splitter: The second transmission waveguide 431 is used to receive and transmit the second signal light, so that the second signal light enters from the second end face of the mode conversion waveguide, and the second signal light is the first mode. The third transmission waveguide 432 is used to receive the third signal light and convert the third signal light into the fourth signal light, so that the fourth signal light enters from the second end face of the mode conversion waveguide 420. Among them, the third signal light is the first mode, the fourth signal light is the first mode, and there is a phase difference between the third signal light and the fourth signal light. The mode conversion waveguide 420 is used to transmit the second signal light to the first end face, and the mode conversion waveguide is also used to convert the fourth signal light into the signal light of the second mode, so that the first signal light is output from the first transmission waveguide. In the first signal light, the signal lights of the first mode and the second mode have the same phase.

[0072] In the case of Figure 4 In the polarization fractionator structure shown, by designing the structures of the first transmission waveguide, the mode conversion waveguide, the second transmission waveguide, and the third transmission waveguide, the mode of the signal light is converted to realize the function of the polarization rotation beam splitter.

[0073] Figure 5 It is a schematic diagram of the mode conversion waveguide structure in a polarization rotation beam splitter provided by an embodiment of the present application. Among them, the cross-section of the mode conversion waveguide along the direction parallel to the substrate has a gradually changing width, that is, the width W of the first end face of the mode conversion waveguide connected to the first transmission waveguide 1 and the width W of the second end face of the mode conversion waveguide connected to the second transmission waveguide (or the third transmission waveguide) 2They are different, so that the mode conversion of the signal light is realized by the gradual change of the width of the mode conversion waveguide.

[0074] In some implementation manners, the cross-section of the mode conversion waveguide along the direction parallel to the substrate may include a plurality of patterns, or it can also be understood that the mode conversion waveguide is composed of multiple segments of waveguides. In some implementation manners, the conversion waveguide is a wedge-shaped waveguide, and the angle θ of the wedge-shaped waveguide is determined according to the actual situation.

[0075] In some implementation manners, as Figure 5 shown in (a) of the figure, the cross-section of the mode conversion waveguide along the direction parallel to the substrate includes a first rectangular region 510, a trapezoidal region 520, and a second rectangular region 530. Among them, the region for realizing the mode conversion of the signal light from the second mode in the first signal light described in Figure 4 to the fourth signal light can be the trapezoidal region 520. In the case shown in Figure 5 , combined with the planar waveguide structure shown in Figure 1 , the conversion of the signal light can be realized within the size of the length L of the mode conversion waveguide being 500 μm. Among them, the conversion form of the signal light can be the conversion between the signal lights of TM0 and TE1.

[0076] In the mode conversion waveguide, the cross-section structures of the waveguide parts corresponding to the first rectangular region 510, the trapezoidal region 520, and the second rectangular region 530 along the direction parallel to the second end face are the same patterns with a gradual change in width. Figure 5 (b) of the figure shows the cross-section of the waveguide part corresponding to the first rectangular region 510 along the direction parallel to the second end face, Figure 5 and (b) of the figure shows the cross-section of the waveguide part corresponding to the first rectangular region 510 along the direction parallel to the second end face. The width of the waveguide cross-section shown in Figure (b) is W 1 , and the width of the waveguide cross-section shown in Figure (c) is W 2 , W 1 <W 2 . The patterns of the cross-section structures of the waveguides shown in Figure (b) and Figure (c) are the same.

[0077] Figure 6 is a schematic diagram of the mode conversion waveguide structure in another polarization rotation beam splitter provided by an embodiment of the present application. The cross-section of the mode conversion waveguide structure along the direction parallel to the substrate is as Figure 6 shown in (a) of the figure, including a first rectangular region 610, a trapezoidal region 620, and a second rectangular region 630. The above regions are similar to those in Figure 5 , and will not be elaborated here.

[0078] In the mode conversion waveguide, the patterns of the cross-sectional structures of the waveguide portions corresponding to the first rectangular region 610, the trapezoidal region 620, and the second rectangular region 630 in the direction parallel to the second end face are different. The cross-section of the waveguide portion corresponding to the trapezoidal region 620 in the direction parallel to the second end face includes a stepped structure. Alternatively, it can also be understood that the top surface width W of the cross-section of the waveguide portion corresponding to the trapezoidal region 620 in the direction parallel to the second end face t is different from the bottom surface width W e . By designing the stepped structure, the symmetry in the vertical direction of the waveguide is broken, so that a hybrid polarization mode is introduced within a small waveguide width W t , the conversion efficiency of the signal light is improved, and the size of the mode conversion waveguide is further reduced.

[0079] The dashed-line portion corresponding to the second rectangular region 630 can be formed by adding one more photolithography and etching step during the photolithography process. Specifically, one more pattern restriction (specific patterns include but are not limited to wedges, diamonds, etc.) is added to the corresponding region of the second rectangular region 630, and after the overall etching of the waveguide is completed, the second rectangular region 630 is etched separately.

[0080] Figure 7 is a schematic structural diagram of the second transmission waveguide and the third transmission waveguide in a polarization rotation beam splitter provided by an embodiment of the present application. As Figure 7 shown, the structures of the second transmission waveguide and the third transmission waveguide can be combined with the mode conversion waveguide shown in Figure 5 and Figure 6 so as to perform mode conversion on the signal light and output it correctly. Among them, by designing the sizes of the second transmission waveguide 710 and the third transmission waveguide 720, optical coupling can be achieved between the second transmission waveguide 710 and the third transmission waveguide 720.

[0081] Taking the situation in Figure 7 as an example, for instance, when the mode conversion waveguide receives the signal light including TE0 and TM0 modes (i.e., the first signal light) and converts the TM0 mode signal light into TE1. The TE1 mode signal light (i.e., the fourth signal light) will enter the second transmission waveguide 710 from the third end face of the second transmission waveguide 710. Since the phase matching condition is satisfied, the TE1 mode signal light (i.e., the fourth signal light) will be coupled into the third transmission waveguide and undergo mode conversion, and the TE0 mode signal light (i.e., the third signal light) will be output from the third transmission waveguide 720. And the TE0 mode signal light will enter the second transmission waveguide 710 from the third end face of the second transmission waveguide 710 and remain unchanged, and be output from the fourth end face of the second transmission waveguide 710.

[0082] Among them, the waveguide width of the second end face where the mode conversion waveguide is connected to the second transmission waveguide 710 can be the same as the width of the third end face of the second transmission waveguide 710, both being W 2 . In the third transmission waveguide 720, specifically, by designing the waveguide width W 4 , optical coupling between the second transmission waveguide 710 and the third transmission waveguide 720 can be achieved, and the phase transformation of the signal light can be completed (for example, transforming the signal light of the TE1 mode into the signal light of the TE0 mode). The length Lc can be referred to as the coupling length, and the length of the length Lc can be reduced by narrowing the spacing d between the second transmission waveguide 710 and the third transmission waveguide 720.

[0083] In some implementation manners, in the second transmission waveguide 710, the width W 2 of the third end face is greater than the width W 3 of the fourth end face. The third end face is the end face connected to the mode conversion waveguide, and the fourth end face is the end face far from the mode conversion waveguide. Thus, by narrowing the width of the second transmission waveguide, the crosstalk between the second transmission waveguide and the third transmission waveguide is further reduced, and the extinction ratio of the polarization mode is improved. The width design of W 3 is based on the first mode. In the case shown in Figure 7 , the width narrowing is completed by the wedge-shaped waveguide 711 with a length of Lt.

[0084] In the structure shown in Figure 7 , the overall length L Figure 4 of the second transmission waveguide and the third transmission waveguide can be combined with the planar optical waveguide structure scheme shown in 2 and controlled within the range of 150 μm to achieve a small-size mode separation scheme.

[0085] Figure 8 is a schematic structural diagram of the second transmission waveguide and the third transmission waveguide in a polarization rotation beam splitter provided by an embodiment of the present application. The structures of the second transmission waveguide and the third transmission waveguide shown in Figure 8 can be combined with the mode conversion waveguide shown in Figure 5 or Figure 6 to perform mode conversion on the signal light and output it correctly. By designing the dimensions of the second transmission waveguide 810 and the third transmission waveguide 820, optical coupling can be achieved between the second transmission waveguide 810 and the third transmission waveguide 820.

[0086] Taking Figure 8Taking the case as an example, for instance, when the mode conversion waveguide receives the signal light including TE0 and TM0 modes (i.e., the first signal light) and converts the signal light of the TM0 mode into TE1. The signal light of the TE1 mode (i.e., the fourth signal light) will enter the second transmission waveguide 810 from the third end face of the second transmission waveguide 810. Since the phase matching condition is satisfied, the signal light of the TE1 mode (i.e., the fourth signal light) will be coupled into the third transmission waveguide and undergo mode conversion, and the signal light of the TE0 mode (i.e., the third signal light) will be output from the third transmission waveguide 820. After the signal light of the TE0 mode enters the second transmission waveguide 810 from the third end face of the second transmission waveguide 810, it remains unchanged and is output from the fourth end face of the second transmission waveguide 810.

[0087] In a cross-section parallel to the substrate direction, the second transmission waveguide 810 includes a first trapezoidal region 811, and the third transmission waveguide 820 includes a second trapezoidal region 821. Among them, one bottom of the first trapezoidal region 811 is connected to the second end face of the mode conversion waveguide, and the second trapezoidal region 821 has a gap from the first trapezoidal region 811. The first waist of the first trapezoidal region is parallel to the second waist of the second trapezoidal structure, and the first waist and the second waist are adjacent.

[0088] Among them, the waveguide width of the second end face where the mode conversion waveguide is connected to the second transmission waveguide 810 can be the same as the width of the third end face of the second transmission waveguide 810, both being W. 2 . In the third transmission waveguide 820, specifically, by designing the upper base W 5 to the lower base W 6 of the second trapezoidal region 821, the optical coupling between the second transmission waveguide 810 and the third transmission waveguide 820 can be realized, and the phase transformation of the signal light can be completed (for example, transforming the signal light of the TE1 mode into the signal light of the TE0 mode). The length Lc can be called the coupling length. By setting the adjacent sides of the coupling region between the second transmission waveguide and the third transmission waveguide to be parallel, the coupling length can be extended, preventing the polarization rotation beam splitter from being affected by process tolerances such as waveguide width and waveguide topography near the coupling region, affecting the performance, and realizing a structural design scheme with high processing tolerance for a polarization rotation beam splitter.

[0089] In some implementation manners, in a cross-section parallel to the substrate direction, trapezoidal regions can be provided in the second transmission waveguide and the third transmission waveguide. The trapezoidal regions serve as transition sections in the waveguide, so that the width of the second transmission waveguide is further narrowed from W 3 to W 4 , and the width of the second transmission waveguide is narrowed from W 6 to W 7 . Thus, by narrowing the widths of the second transmission waveguide and the third transmission waveguide, the crosstalk between the second transmission waveguide and the third transmission waveguide can be further reduced, and the extinction ratio of the polarization mode can be improved.

[0090] In some implementations, in a cross-section parallel to the substrate direction, the second transmission waveguide 810 and the third transmission waveguide 820 are isosceles trapezoids. That is, the first trapezoidal region 811 and the second trapezoidal region 821 have the same pattern shape and are arranged in opposite directions, thereby lengthening the coupling length and realizing a structural design solution with high processing tolerance for a polarization rotation beam splitter.

[0091] In a structure as Figure 8 shown, a planar optical waveguide structure solution as Figure 4 shown can be combined to control the overall length L 3 of the second transmission waveguide and the third transmission waveguide within a range of 500 μm, realizing a small-size mode separation solution.

[0092] Figure 9 This is an optical chip provided by an embodiment of the present application. In some implementations, as Figure 9 shown in (a) therein, the optical chip may include an orthogonal modulator and a polarization rotation beam splitter. As Figure 9 shown in (b) therein, the optical chip may include a polarization rotation beam splitter and a coherent receiver. Among them, the polarization rotation beam splitter may be a planar optical waveguide structure as Figure 1 described therein, or Figures 5 to 8 a polarization rotation beam splitter structure as Figure 1 described therein, or Figures 5 to 8 combinations may be made between the structures described therein, or combinations may be made with other forms of waveguides or structures, and the present application does not limit this.

[0093] In a structure as Figure 9In the case shown in (a), the orthogonal modulator 910 can be used to modulate the signal light to transmit two paths of signal light to the polarization rotation beam splitter 930. The two paths of signal light are the second signal light and the third signal light respectively. The second signal light is in the first mode, and the third signal light is in the first mode. Among them, the orthogonal modulator 910 can be the Mach-Zehnder modulator in the figure. The Mach-Zehnder modulator can be specifically used to modulate the frequency, amplitude, etc. of the signal light. The second signal light and the third signal light output from the orthogonal modulator 910 can carry different or the same information respectively. The polarization rotation beam splitter is used to receive the second signal light and the third signal light, and combine the second signal light and the third signal light to output the first signal light. The first signal light includes the signal light in the first mode and the signal light in the second mode. The first mode can be TE0, and the second mode can be TM0. In some implementation manners, a waveguide converter 920, or it can also be understood as a transition waveguide, is further provided in the optical chip. The waveguide converter is used to connect the orthogonal modulator 910 and the polarization rotation beam splitter 930, and the waveguide converter is arranged between the orthogonal modulator 910 and the polarization rotation beam splitter 930. In addition, a light source can also be provided in the optical chip, and the light source is connected to the orthogonal modulator 910. At this time, the optical chip can be a chip in the form of an optical transmitter, that is, an optical transmitter chip.

[0094] In the case as Figure 9 shown in (b), the polarization rotation beam splitter can be used to receive the first signal light. The first signal light includes the signal light in the first mode and the signal light in the second mode, and split the first signal light into two paths to output the second signal light and the third signal light. Among them, the second signal light is in the first mode, the third signal light is in the first mode, and the second signal light and the third signal light can carry the same or different information. The second signal light among them is received by the coherent receiving unit 941, and the third signal light is received by the coherent receiving unit 942. The coherent receiving unit 941 and the coherent receiving unit 942 form a coherent receiver. The coherent receiver is used to demodulate the second signal light and the third signal light to obtain the electrical signal corresponding to the second signal light and the electrical signal corresponding to the third signal light. Among them, each of the coherent receiving unit 941 and the coherent receiving unit 942 can specifically include a mixer, a photodetector, and a passive optical waveguide. In some implementation manners, a waveguide converter 920, or it can also be understood as a transition waveguide, is further provided in the optical chip. The waveguide converter is used to connect the polarization rotation beam splitter and the coherent receiving unit 941 or the coherent receiving unit 942, and the waveguide converter is arranged between the polarization rotation beam splitter and the coherent receiving unit 941 or the coherent receiving unit 942. At this time, the optical chip can be a chip in the form of an optical receiver, that is, an optical receiver chip.

[0095] In the case as Figure 9The optical chip shown is applied to the coherent optical communication scenario. The signal light in the first mode can also be understood as the signal light with X polarization, and the signal light in the second mode can also be understood as the signal light with Y polarization.

[0096] Figure 10 This is an optical module provided by an embodiment of the present application. The optical module may include an optical chip in two forms as shown in Figure 9 (a) or (b) below.

[0097] In some implementation manners, as shown in Figure 10 (a) below, the optical module includes a light source 1010, an optical chip 1020, and a signal generation chip 1030. The specific structure of the optical chip 1020 is similar to that in Figure 9 (a) below and will not be described in detail here. At this time, the optical module may specifically refer to an optical transmission module. Among them, the light source 1010 is used to input a light beam into the quadrature modulator 1021 in the optical chip. The signal generation chip 1030 is used to input an electrical signal into the quadrature modulator 1021. The electrical signal is used to modulate the light beam input into the quadrature modulator 1021 to generate a second signal light and a third signal light carrying information. The second signal light and the third signal light carrying information are input into the polarization rotation beam splitter 1022. The polarization rotation beam splitter 1022 is used to combine the second signal light to output a first signal light including a first mode and a second mode. The signal generation chip may specifically integrate a digital signal processing (DSP) module, a digital-to-analog conversion (DAC) module, etc., which is determined according to the actual situation. In the case of Figure 10 (a) below, the light source 1010 and the optical chip 1020 are discrete components. The light source 1010 may specifically refer to coherent light.

[0098] In some implementation manners, as shown in Figure 10 (b) below, the optical module includes a light source 1010, an optical chip 1020, and a signal generation chip 1030. Figure 10 The light source 1010, the optical chip 1020, and the signal generation chip 1030 shown in Figure 10 (b) below are similar to those in Figure 10 (a) below and will not be described in detail here. In the case of

[0099] In some implementation manners, as shown in Figure 10 (c) below, the optical module includes an optical chip 1040 and a signal processing chip 1050. The specific structure of the optical chip 100 is similar to that in Figure 10Similar to that in (c), details are not repeated here. At this time, the optical module may specifically refer to an optical receiving module. Among them, the polarization rotation beam splitter 1041 is used to receive the first signal light including the first mode and the second mode, and output the second signal light and the third signal light carrying information. The second signal light is the first mode, and the third signal light is the first mode. The coherent receiver 1042 is used to convert the second signal light into the first electrical signal and convert the third signal light into the second electrical signal. The signal processing chip 1040 is used to process the first electrical signal and the second electrical signal to obtain the information carried in the second signal light and the information carried in the third signal light. The signal processing chip 1050 may specifically integrate an analog-to-digital conversion (ADC) module, a digital signal processing (DSP) module, etc., which is determined according to the actual situation.

[0100] In addition, as Figure 10 shown in (c), the optical module can be combined with Figure 10 the optical module in (a) or Figure 10 the optical module in (b), etc. to obtain an optical transceiver module.

[0101] Figure 11 This is an optical communication system provided by an embodiment of the present application. As Figure 11 shown, the optical system may include an optoelectronic device and an optical module as Figure 10 shown. Among them, the optoelectronic device 1110 may be any one of an optical switch, an optical fiber router, and an optical fiber network card. The optoelectronic device 1110 is connected to the optical module 1020.

[0102] The optoelectronic device may include multiple ports. Each port among the multiple ports corresponds to an optical transmission channel. The ports among the multiple ports are connected to the optical module, thereby realizing multi-channel and high-rate signal light transmission. Among them, the optical switch can be used to realize data exchange between multiple optical transmission channels. The optical fiber router can be used to convert the signal light into a data signal and realize the forwarding and routing selection of the data signal. The optical fiber network card can be used in an Ethernet network to realize the connection between a computer and an optical fiber.

[0103] Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, or by a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of this application.

[0104] As described above, it is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claimed rights.

Claims

1. A planar optical waveguide, characterized in that, it comprises, arranged successively from bottom to top: a substrate; a sacrificial layer, including at least one air cavity that penetrates from the bottom surface to the top surface of the sacrificial layer; a core layer, including a polarization rotation beam splitter.

2. The planar optical waveguide according to claim 1, characterized in that, wherein: an upper cladding is further provided in the planar optical waveguide, the upper cladding is located above the core layer, and the refractive index of the upper cladding is less than that of the core layer; and / or a lower cladding is further provided in the planar optical waveguide, the lower cladding is located between the core layer and the sacrificial layer, and the refractive index of the lower cladding is less than that of the core layer.

3. The planar optical waveguide according to claim 1 or 2, characterized in that, at least one etching hole is provided in the planar optical waveguide, and the etching hole penetrates from the top surface of the planar optical waveguide to the top surface of the sacrificial layer.

4. The planar optical waveguide according to any one of claims 1 to 3, characterized in that, on the substrate, the projection of the core layer covers the projection of the air cavity.

5. The planar optical waveguide according to any one of claims 1 to 4, characterized in that, a support layer is further provided in the planar optical waveguide, the support layer is located above the core layer, the support layer is at least partially in contact with the core layer, and on the substrate, the projection of the support layer covers the projection of the air cavity.

6. The planar optical waveguide according to any one of claims 1 to 5, characterized in that, the polarization rotation beam splitter includes a first transmission waveguide, a mode conversion waveguide, a second transmission waveguide and a third transmission waveguide, wherein: the first transmission waveguide is connected to the first end face of the mode conversion waveguide; the second transmission waveguide is connected to the second end face of the mode conversion waveguide; the projection of the second transmission waveguide on a first plane overlaps with the projection of the third transmission waveguide, the first plane is perpendicular to the plane where the substrate is located, and the first plane is parallel to the light transmission direction of the polarization rotation beam splitter.

7. The planar optical waveguide according to claim 6, characterized in that, the cross-section of the mode conversion waveguide in the direction parallel to the substrate includes a trapezoidal region, and in the waveguide portion of the mode conversion waveguide corresponding to the trapezoidal region, the cross-section in the direction parallel to the second end face is a stepped structure.

8. The planar optical waveguide according to claim 6 or 7, characterized in that, the width of the third end face of the second transmission waveguide is greater than the width of the fourth end face, where the third end face is the end face connected to the mode conversion waveguide, and the fourth end face is the end face far from the mode conversion waveguide.

9. The planar optical waveguide according to any one of claims 6 to 8, characterized in that, in the cross-section of the core layer in the direction parallel to the substrate, the second transmission waveguide includes a first trapezoidal region, and the third transmission waveguide includes a second trapezoidal region, wherein one bottom of the first trapezoidal region is connected to the second end face, the first waist of the first trapezoidal region is parallel to the second waist of the second trapezoidal region, and the first waist and the second waist are adjacent.

10. The planar optical waveguide according to claim 9, wherein, the first trapezoidal region and the second trapezoidal region are isosceles trapezoids.

11. A method for manufacturing a planar optical waveguide, wherein, it is used to manufacture the planar optical waveguide according to any one of claims 1 to 10.

12. An optical chip, wherein, it includes an orthogonal modulator and the planar optical waveguide according to any one of claims 1 to 10.

13. An optical chip, wherein, it includes a coherent receiver and the planar optical waveguide according to any one of claims 1 to 10.

14. An optical module, wherein, it includes: a light source, a signal generation chip, and the optical chip according to claim 12; and / or a signal processing chip and the optical chip according to claim 13.

15. An optical communication system, wherein, it includes an optoelectronic device and the optical module according to claim 14, wherein the optoelectronic device is connected to the optical module, and the optoelectronic device is any one of an optical switch, a fiber router, and a fiber network card.

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